REFERENCE TO RELATED APPLICATIONS NA
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The present invention relates to forklift trucks, and in particular, relates to an improved method and apparatus for preventing fog and condensation from accumulating on a windshield of a forklift truck that traverses between environments having varying temperatures.
When operating a forklift vehicle at high speeds in cold storage environments, whose temperatures can typically reach as low as xe2x88x9225xc2x0 F., a significant wind chill is experienced by the operator, thereby causing discomfort. It is therefore desirable to install a windshield in the truck that will protect the operator from the winds associated with operation of the forklift truck in the cold environment and reduce operator discomfort.
However, because forklift trucks typically traverse between cold storage applications and warm environments, the windshield may experience significant temperature differentials of more than 100xc2x0 F. Moreover, due to the cold air flow within the cold storage application, various locations on the windshield may be colder than others. Additionally, because the temperature of the cold storage application is commonly less than the dew point of the warmer environment, condensation will accumulate on the windshield when the truck travels from the cold storage application into the warmer environment, thereby obstructing the operator""s view. Subsequently, when the truck travels back into the cold environment, the condensation will freeze on the windshield, thereby further obstructing the operator""s view, and in most cases rendering the forklift truck unavailable for an extended amount of time.
As a result of the significant drawbacks currently associated with installing a windshield on forklift trucks that traverse between environments having significantly varying temperatures, a wire mesh is conventionally used in place of a windshield so as to prevent condensation from obstructing the operator""s view. However, the wire mesh inadequately shields the operator from the potentially severe wind chills that are produced during operation of the forklift truck. Additionally, the wire mesh introduces partial obstruction of the view of the operator. It is therefore desirable to provide a heated windshield assembly, thereby avoiding the disadvantages associated with the wire mesh.
Conventional heated windshield assemblies supply heat to a window having only one surface exposed to the ambient environment, with the other surface disposed within a heated enclosure, such as the interior of a vehicle. Accordingly, in these devices, it is not necessary or desirable to maintain the inner and outer surfaces of the window at substantially the same temperature. Rather, it is only necessary to heat the outer surface of the window that is exposed to the ambient environment. As a result, if such assemblies were to be installed onto an open forklift truck, having both surfaces of the windshield exposed to the ambient environment, only one surface would be protected from condensation. This would inadequately protect the windshield from condensing when the truck travels into the warmer environment, and subsequently freezing when the truck travels back into the cold storage application.
What is therefore needed is a method and apparatus for supplying heat equally to both sides of a windshield assembly and to ensure that condensation does not accumulate thereon when the truck traverses between cold and warm environments.
In accordance with a first aspect of the invention, a windshield member is mounted to a vehicle having first and second surfaces exposed to the ambient environment, wherein the first surface faces an operator console and the second surface faces away from the operator console, a heating assembly disposed within the windshield member and configured to supply heat thereto, a first temperature sensor mounted onto the windshield member at a first location and being operable to output a first temperature signal indicating the temperature thereof, a second temperature sensor mounted on to the windshield member at a second location different than the first location and being operable to output a second temperature signal indicating the temperature thereof, and a controller in electrical communication with the heating elements and the first and second temperature sensors and being operable to supply electrical power to the heating assembly when the either sensor indicates a temperature that is below a predetermined temperature level.
In accordance with another aspect of the invention, the predetermined threshold temperature is chosen to be above the dew point of the second location. The present inventor has recognized that heating elements may be installed in a transparent windshield of an open vehicle to maintain the windshield at a predetermined temperature relative to the dew point of the outside or other warm environment to prevent condensation from accumulating on the windshield, and to reduce the wind chill that is typically experienced by the operator of the vehicle. Accordingly, when the vehicle is moved from the cold environment into the warmer environment, condensation will not accumulate on the windshield, thereby preserving the operator""s field of view.
These as well as other features and characteristics of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described with reference to the accompanying drawings. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments, and reference should therefore be made to the claims herein for interpreting the breadth of the invention.